1. Field of the Invention
The present general inventive concept relates to an apparatus to sense the temperature of a hyperfine/high resolution ink-jet head so as to precisely control the temperature of micro-parts such as a precision machine/a micro-electro-mechanical systems (MEMS) chip, etc.
2. Description of the Related Art
All conventional shuttle/array type ink-jet printers require control of temperature of ink to a predetermined level because, in current ink-jet printers, the ink suffers a change in viscosity due to the temperature of a head chip and the temperature of an ambient environment.
A change in viscosity of ink due to the temperature affects a drop volume of ink ejected from an ink-jet head chip and thus affects the quality of an image printed on a print medium such as paper, etc. For example, an amount of ink ejected, having decreased viscosity as the temperature increases, increases according to unit nozzles. Thus, an optical density of ink increases. On the contrary, the amount of ink ejected, having increased viscosity as the temperature decreases, is reduced according to unit nozzles. Thus, the optical density of ink decreases.
In addition, a result of repeated output in a high speed/high resolution mode causes a gradual temperature rise in an ink-jet head chip. At more than a predetermined temperature, the result of stabilized ejection cannot be predicted. Thus, at more than a predetermined temperature, time for stopping an operation and for reducing the temperature of the ink-jet head chip is required. In general, the environment in which a current ink-jet head chip is used, has a temperature between −20° C. to 40° C. When there is no additional control of repeated ejection in an ink-jet printer, the temperature inside the ink-jet head chip may continuously increase. Thus, in order to eject the amount of ink to a predetermined level of accuracy regardless of the ambient environment, a function of adjusting the ink-jet head chip within a predetermined range of temperature when ink is ejected is needed. In particular, in the case of a printer having a wide array head chip using an array type head chip (not a shuttle type head chip), the temperature between adjacent head chips is changed. A difference in temperature between adjacent head chips may cause remarkable image defects.
Thus, in the case of a printer using a wide array head chip, more precise temperature control is needed. To this end, a temperature sensor is used. As an example of a temperature sensor, a thermistor or a diode is used. The thermistor is used in a temperature sensing method using the principle that a change in resistance occurs according to temperature. However, a temperature sensor using a thermistor has a variation width of sensor resultant values and thus, sensor correction is needed. In addition, the temperature sensor using the thermistor has a drawback of the head chip having a large area. Meanwhile, a temperature sensor using a diode measures the temperature by a forward bias voltage being applied to a current supplied through an additional current source circuit and a voltage changing according to the temperature. However, in such a temperature sensor using a diode, an additional mask and an additional process must be additionally used when a monolithic type ink-jet head having an integrated complementary metal oxide semiconductor (CMOS) is designed or processed. In addition, a diode needs a predetermined area unlike a transistor which can be easily refined, and thus the diode occupies a large area of a silicon substrate.
In order to solve this problem, a metal oxide semiconductor field effect transistor (MOSFET) or a bipolar junction transistor (BJT) is used as a temperature sensor. In order to obtain a linear relationship between the temperature and the MOSFET, the MOSFET must operate in a weak channel inversion band. However, a leakage current and variations in process distortion and threshold voltage of the MOSFET at high temperatures are large. Thus, an additional correction operation is needed. In the BJT, a base-emitter junction potential indicates the linear characteristic of voltage/temperature. Thus, a bipolar CMOS (BiCMOS) having functions of a BJT type temperature sensor and a CMOS temperature sensor may be used. However, manufacturing costs of the BiCMOS are high.